A. Field of the Invention
In continuous metal casting machines such as twinbelt casting machines, the molten metal being cast is fed into a casting region between opposed portions of a pair of revolving flexible, liquid-cooled belts, the liquid coolant usually being water containing rust inhibitors. The moving belts, in cooperation with moving side dams(often called "edge dams"), confine the molten metal between them and carry the molten metal along as it solidifies. Spaced back-up rollers having narrow ridges support the belts and also guide the belts as they move along through the casting region. The large quantities of heat liberated by the molten metal as it solidifies are withdrawn through those portions of the belts and side dams which are adjacent to the metal being cast.
Each of the two flexible casting belts revolves around a belt carriage in a path defined by main pulleys located in the carriage around which the belt passes. In some twin-belt casting machines there are two main pulleys at opposite ends of the carriage defining a racetrack path for the belt to travel. Other twin-belt casting machines have three or more main pulleys in each carriage defining the belt path.
The molten metal in the input region of a twin-belt machine may advantageously be shrouded with inert gas by means of suitable application techniques, while at the same time using the inert gas for purging the approaching casting belts of reactive gases, as disclosed in copending U.S. patent application Ser. No. 372,459 of Robert Wm. Hazelett, Charles J. Petry and Stanley W. Platek dated Apr. 28, 1982 and assigned to the same assignee as the present invention.
For further information about twin-belt casting machines in general, the reader may refer to one or more of the following U.S. Pat. Nos. 2,640,235; 2,904,860; 3,036,348; 3,041,686; 3,123,874; 3,142,873; 3,167,830; 3,228,072; 3,871,905; 3,937,270; 4,002,197; and 4,082,101.
The present invention particularly concerns the side dams or edge-dam blocks in the above-described casting machines. These side or edge dams are assembled from multiplicity of blocks which, for instance, may be slotted and strung onto a flexible metal strap as described in U.S. Pat. Nos. 2,904,860; 3,036,348; and 3,955,615. In place of the metal strap, metal cables have also been used.
B. Prior Art
Prior art, notably that of belt preheating as described in U.S. Pat. Nos. 3,937,270; 4,002,197; and 4,082,101 has improved the overall shape, soundness, and metallurgy of strip or slab cast continuously between twin flexible belts. Also, belt coating consisting of resins containing fillers of finely divided insulating or finely divided particles of refractory materials have proved helpful, as described in U.S. Pat. No. 3,871,905. The heat transferred to the belts from the freezing or solidifying metal would cause temporary longitudinal flutes (transversely spaced hills and valleys), which were observed to be wide and deep in both the product being cast and in the casting belts themselves. The above-mentioned techniques controlled this belt distortion problem.
In spite of apparently solving the belt-distortion problem, shallow, straight, longitudinal "sinks" appeared in the top of the slab or strip. The sinks would run continuously and were centered typically at a distance of three to seven times (and sometimes up to nine times) the slab thickness from either edge, independent of the width of the slab being cast. The resulting deformed or distorted cross-section has been referred to as a "dog-bone" shape or phenomenon. This dog-bone problem, though not so dramatic in appearance in the cast slab as the longitudinal flutes caused by belt distortion, is nevertheless a significant barrier to the attainment of product of high quality. The present invention solves the dog-bone problem by eliminating or substantially eliminating such longitudinal sinks, and therefore, this invention opens up important new applications for continuous casting in twinbelt casting machines.